css 一个问题

我希望按照 .pic_upload 中指定的大小一行行排开，按道理占位应该是一个正方形，为什么确交错了？




 .pic_upload
 {
     width:184;
     height:184;
     float:left;
     margin:20px 0 0 20px;
     border:2px solid #5FA9E1;
  }

<div id="picload">

<div class="pic_upload"><img src="/Pic/20131205/30424786-15b5-4ab2-a027-c898e7c21c01/m.jpg" alt=""></div>



<div class="pic_upload"><img src="/Pic/20131205/055642e6-b06f-4b09-8117-2840d0e677c4/m.jpg" alt=""></div>



<div class="pic_upload"><img src="/Pic/20131205/4c507710-3fa2-4fc5-ad5f-ca621dc3ed6b/m.jpg" alt=""></div>



<div class="pic_upload"><img src="/Pic/20131205/d7b56f62-b408-41ff-a635-668a048e2348/m.jpg" alt=""></div>



<div class="pic_upload"><img src="/Pic/20131205/d39c2238-f116-4c94-9ead-e203e35433b2/m.jpg" alt=""></div>



<div class="pic_upload"><img src="/Pic/20131205/f68d0b7b-e29d-4719-a003-8a3ec1871e6a/m.jpg" alt=""></div></div>

------解决方案--------------------

.pic_upload

 {

     width:184px;

     height:184px;

     float:left;

     margin:20px 0 0 20px;

     border:2px solid #5FA9E1;

  }

没加上单位..